By Ben Winkley

LONDON--The future of the U.K.'s Grangemouth oil refinery hangs in the balance, with shareholders due to meet later Tuesday after the workers' union said two-thirds of its members had rejected the company's plan for the plant.

The Unite labor union said 665 of the 1,400-strong workforce had not signed up to operator Ineos' proposals to freeze pay and change the pension plan. The company had set Monday evening as a deadline for responses.

Ineos began shutting the plant, Scotland's only refinery and a vital conduit for around 45% of total North Sea crude-oil output, when Unite announced a 48-hour strike from Oct. 20. This was subsequently called off after conciliation talks, but Ineos refused to restart the facility unless it received a guarantee of no further strikes. Swiss-based Ineos has previously said Grangemouth was losing 10 million pounds ($16.0 million) a month, and it is in talks with the Scottish and U.K. governments about grants.

Ineos said it will present the results of the workforce consultation to its shareholders, which include PetroChina Co. (601857.SH), later Tuesday and will convey the outcome of that meeting to the workforce on Wednesday.

In a statement, Unite urged Ineos' management to resume talks, describing the results of the consultation as "an overwhelming rejection of the company's blackmail and threats."

The 210,000 barrels-a-day Grangemouth refinery provides most of the fuel for Scotland and northern England. Heat from the refinery and the neighboring petrochemicals plant powers BP PLC's (BP) Kinneil oil terminal, which processes North Sea crude coming ashore through the Forties Pipeline System.

Write to Ben Winkley at ben.winkley@wsj.com

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